Winter D, Polacek N, Halama I, Streicher B, Barta A
Institute of Biochemistry, University of Vienna, Vienna Biocenter, Dr Bohr-Gasse 9/3, A-1030 Vienna, Austria.
Nucleic Acids Res. 1997 May 1;25(9):1817-24. doi: 10.1093/nar/25.9.1817.
Ribosomes have long been known to require divalent metal ions for their functional integrity. Pb2+-induced cleavage of the sugar-phosphate backbone has now been used to probe for metal binding sites in rRNA. Only three prominent Pb2+cleavages have been detected, with cleavage sites 5' of G240 in 16S rRNA and two sites 5' of A505 and C2347 in 23S rRNA. All cleavages occur in non-paired regions of the secondary structure models of the rRNAs and can be competed for by high concentrations of Mg2+, Mn2+, Ca2+ and Zn2+ ions, suggesting that lead is bound to general metal binding sites. Although Pb2+ cleavage is very efficient, ribosomes with fragmented RNAs are still functional in binding tRNA and in peptidyl transferase activity, indicating that the scissions do not significantly alter ribosomal structure. One of the lead cleavage sites (C2347 in 23S RNA) occurs in the vicinity of a region which is implicated in tRNA binding and peptidyl transferase activity. These results are discussed in the light of a recent model which proposes that peptide bond formation might be a metal-catalysed process.
长期以来，人们都知道核糖体需要二价金属离子来维持其功能完整性。现在，Pb2+诱导的糖磷酸骨架断裂已被用于探测rRNA中的金属结合位点。仅检测到三个显著的Pb2+切割位点，分别位于16S rRNA中G240的5'端，以及23S rRNA中A505和C2347的5'端的两个位点。所有切割都发生在rRNA二级结构模型的非配对区域，并且可以被高浓度的Mg2+、Mn2+、Ca2+和Zn2+离子竞争，这表明铅与一般的金属结合位点结合。尽管Pb2+切割非常有效，但RNA片段化的核糖体在结合tRNA和肽基转移酶活性方面仍然具有功能，这表明切割并没有显著改变核糖体结构。其中一个铅切割位点（23S RNA中的C2347）位于一个与tRNA结合和肽基转移酶活性有关的区域附近。根据最近提出的肽键形成可能是一个金属催化过程的模型，对这些结果进行了讨论。
